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If your chestnuts are afflicted by worms, they’re most likely infested by one of two species of chestnut weevils, a kind of beetle. "Worms" is a term sometimes applied to what are more commonly called grubs, the weevil larvae. Lesser and greater chestnut weevils have similar life cycles and do the same kind of damage. The means of controlling them are also similar.

What The Weevils Look Like

As the burrs surrounding both American and Chinese chestnuts begin to crack in the summer, light tan to dark brown chestnut weevils, beetles with hard shells, lay eggs in the downy inner lining of the burrs. American chestnuts (Castanea dentate) grow in U.S. Department of Agriculture plant hardiness zones 4 to 8. Chinese chestnuts (Castanea Mollissima) grow in USDA zones 5 through 8. Other than their size, chestnut weevils are difficult to distinguish. Lesser chestnut weevils (Curculio sayi) are from 1/4 to 1/2 inch long. Larger chestnut weevils (Curculio caryatrypes) are about 3/8 inch long with 5/8-inch-long female beaks and 1/4-inch-long male beaks.

How They Live

Chestnut weevil eggs hatch about 10 days after they’re laid. The newly hatched, cream-colored grubs begin tunneling into the nut kernels. Greater weevil grubs chew through the nut shells and fall to the ground before nuts drop in late summer or early autumn. Lesser weevil grubs eat through the shells after the nuts drop. Once on the ground, grubs of both species burrow into the soil where they spend the winter, emerging as adults the following spring. Come summer, they lay their eggs in the burrs that envelop maturing chestnuts. The weevils spend two winters in the ground and die after their second round of laying eggs.

Dealing With Them Naturally

Collect chestnuts within two to three days after they hit the ground and sooner than that if you can. Gather and destroy all leaves and fallen burrs as well. To kill weevil eggs or small grubs in the nuts without affecting the ability of the nuts to germinate, immerse them for 20 minutes in water heated to 120 degrees Fahrenheit. Weevil grubs can survive heat up to 117 F.

Killing Them With An Insecticide

Adult chestnut weevils drop from the tree easily. To find out if your tree is infected, spread a sheet under the tree and shake the branches vigorously. Chestnut weevils head for early ripening trees, so check those first. Spray your trees with an insecticide containing the active ingredient carbaryl beginning in late July when weevils begin landing to lay eggs. Spray four weekly applications at the rate of 3 to 3 3/4 ounces per 1,000 square feet. Wear socks, trousers, a long-sleeved shirt, goggles and a hat that you can wash. Do not get carbaryl in your eyes.